The present invention relates to pressure measuring apparatus in general and in particular to a novel, portable, reliable, rugged and inexpensive water pressure gauge for measuring depth of water or altitude in air. Gauges of the type described are frequently used in relatively deep submarine work by divers for indicating the depth of water at which the divers are working. Such gauges are also widely used by recreational divers.
Generally, the gauges used heretofore in diving employ an aneroid mechanism or conventional Bourdon tube with suitable linkage and an indicator calibrated to provide a display of depth in feet or meters as a function of ambient water pressure. Typical of the gauges of these types are the gauges described in U.S. Pat. Nos. 3,693,446; 3,828,611 and 3,203,244.
Bourdon type gauges are quite accurate and widely used but are relatively expensive to manufacture to achieve the same precision of spring rate as that obtained with a common spring.
The internal mechanism in the Bourdon gauges is also relatively delicate and, therefore, care must be taken to insure that they are not unduly subjected to shocks or external loads. For example, Bourdon tube-driven needles in depth gauges are severely affected by even the slightest resistance of a secondary needle, such as the maximum depth indicator. Indeed, a secondary needle can cause the primary depth needle to read typically 3% lower than it would in the absence of the secondary needle.
For these reasons, it is desirable to have a gauge with a maximum depth indicator which is portable, relatively accurate over a wide range of water depths, rugged, reliable and relatively inexpensive.